Fewer than 5,000 Islamic State fighters trying to hold onto the Iraqi city of Mosul are being urged to fight to the death.
"Know that holding your ground with honor is a thousand times easier than retreating in shame," the terror group's leader and self-declared caliph Abu Bakr al-Baghdadi exhorted in an audio recording released via social media late Tuesday.
"Do not retreat," he said. "This total war and the great jihad only increased our firm belief, God willing, and our conviction that this is all a prelude to victory."
The message from Baghdadi is the first since last December and comes nearly three weeks into the Iraqi and Kurdish campaign to retake Mosul, which has been under IS control for two years.
U.S. intelligence sources say there is no reason to doubt the audio's authenticity and agree, based on the content of the remarks, it was likely made recently.
IS command and control
A U.S. military spokesman in Iraq said officials there were not yet ready to verify that the voice on the recording was that of the IS leader but acknowledged the message was clearly "an effort to rally the troops."
"This is the type of thing that a leader who's losing command and control and ability to keep everybody on the same page says," Operation Inherent Resolve spokesman, Col. John Dorrian told reporters via a video conference from Baghdad.
"We don't believe that it's going to work," he added.
But intelligence officials believe the recording may also be intended to dispel any notions or rumors the reclusive Baghdadi has been killed.
Some analysts examining the pacing and the rhetoric in the audio message think the significance of the recording could be even greater, suggesting a key shift in the way IS has been fighting up until now.
"Abu Bakr al-Baghdadi's statement is the fastest in tempo and strongest among his speeches," according to a Tweet by Hassan Hassan, a resident fellow at the Tahrir Institute for Middle East Policy who has written extensively about IS.
"The new tone/message tells us clearly that ISIS wants the remaining strongholds to be a big show," Hassan added in another tweet. "It won't withdraw as it did before."
Choosing their fights
There are indications that IS fighters are prepared to make such a stand in spite of overwhelming odds.
"They don't seem to be panicking," a U.S. official told VOA.
The official, speaking on the condition of anonymity, said despite the faster than expected advance of Iraqi and Kurdish forces, IS fighters in and around Mosul were showing no signs of abandoning their training or giving up their well-known tactics.
U.S. defense officials also say it appears IS is picking its fights carefully.
"In some villages, they slice through them like butter, and there's very little resistance at all, and ISIL up and leaves," Pentagon spokesman, Capt. Jeff Davis said Wednesday when asked about the type of resistance Iraqi and Kurdish forces were encountering around Mosul.
"There are others that put up quite a fight," he added.
Even civilians who have been rescued from IS say there are few signs the terror group is ready to fall apart.
"I spoke to this large group of civilians who had been marched by ISIS north," said Human Rights Watch senior Iraq researcher Belkis Wille after visiting with civilians at Jeddah camp, near Qayyarah airfield south of Mosul.
"They made it sound fairly organized," she said. "ISIS came door to door, knocked on each door, told people they had to leave. They had vehicles kind of patrolling the group as they were walking."
The question is just how long the group will be able to maintain that type of coherence, with the toughest and bloodiest fighting still ahead.
And while in the past IS fighters have often fled in the face of overwhelming force, that may not be the case for those forces left in Mosul.
"If they're still in Mosul, given that they've known there's a massive buildup of troops in that area, that means they probably want to fight till the end," said former CIA analyst Aki Peritz, now with George Washington University's Center for Cyber and Homeland Security.
And with the number of likely escape routes shrinking, IS fighters may not have much of a choice.